A radio frame in a Long Term Evolution (LTE) system may have a frame structure of a Frequency Division Duplex (FDD) mode or a frame structure of a Time Division Duplex (FDD) mode. For the frame structure of FDD mode, as shown in FIG. 1, a 10 ms radio frame is composed of 20 time slots, all of which have a length of 0.5 ms and are numbered from 0 to 19, and time slots 2i and 2i+1 form subframe i with a length of 1 ms. For the frame structure of TDD mode, as shown in FIG. 2, a 10 ms radio frame is composed of two half frames with a length of 5 ms, each half frame comprises 5 subframes with a length of 1 ms, subframe i is defined as two time slots 2i and 2i+1 with a length of 0.5 ms. In the above two frame structures, for a Normal Cyclic Prefix (Normal CP), a time slot comprises 7 symbols with a length of 66.7 μs, wherein the CP length of the first symbol is 5.21 μs, and the CP length of each of the remaining 6 symbols is 4.69 μs; for an Extended Cyclic Prefix (Extended CP), a time slot comprises 6 symbols, with the CP length of each of these symbols being 16.67 μs.
The version number of the LTE corresponds to R8 (Release 8) and its enhanced version corresponds to the version number R9 (Release 9). The LTE defines the following three types of downlink physical control channels: a Physical Control Format Indicator Channel (PCFICH); a Physical Hybrid Automatic Repeat Request Indicator Channel (PHICH); and a Physical Downlink Control Channel (PDCCH).
The information carried by the PCFICH is used for indicating the number of Orthogonal Frequency Division Multiplexing (OFDM) symbols for transmitting the PDCCH in a subframe and is sent by the first OFDM symbol of the subframe, and a frequency location of the information is determined by the system downlink bandwidth and a cell identity (ID).
The PHICH is for carrying ACK/NACK feedback information of uplink transmitted data. The number and time-frequency location of the PHICH may be determined by a system message and a cell ID in a Physical Broadcast Channel (PBCH) of a downlink carrier where the PHICH is located.
The PDCCH is for carrying Downlink Control Information (DCI) which comprises uplink and downlink scheduling information, and uplink power control information. The DCI Format comprises DCI Format 0, DCI Format 1, DCI Format 1A, DCI Format 1B, DCI Format 1C, DCI Format 1D, DCI Format 2, DCI Format 2A, DCI Format 3, DCI Format 3A, etc.
DCI Format 0 is for indicating scheduling of a Physical Uplink Shared Channel (PUSCH);
DCI Format 1, DCI Format 1A, DCI Format 1B, DCI Format 1C, and DCI Format ID are for indicating different modes of scheduling of one PDSCH codeword;
DCI Format 2 and DCI Format 2A are for indicating diffident modes of space division multiplexing;
DCI Format 3 and DCI Format 3A are for indicating different modes of power control instructions of a Physical Uplink Control Channel (PUCCH) and a PUSCH.
Further, information transmitted in DCI Format 1A is as follows:
(1) 1 bit for selecting DCI Format 0 or DCI Format 1A;
(2) 1 bit for selecting a resource assignment scheme of a Localized Virtual Resource Block (LVRB) or a Distributed Virtual Resource Block (DVRB);
(3) ┌ log2 (NRBDL(NRBDL+1)/2)┐ bits for resource block assignment, wherein NRBDL denoting a downlink bandwidth, represented by the number of Resource Blocks (RB);
(4) 5 bits for indicating a Modulation and Coding Scheme (MCS);
(5) in an FDD system, 3 bits for indicating Hybrid Automatic Repeat Request (HARQ) process number; in a TDD system, 4 bits for indicating HARQ process number;
(6) 1 bit for a New Data Indicator (NDI);
(7) 2 bits for indicating a redundant Version (RV);
(8) 2 bits for Transmit Power Control (TPC) of the PUCCH;
(9) 2 bits for Downlink Assignment Index (DI), which is only needed in uplink and downlink configuration of the TDD system, but is not needed in the FDD system; and
(10) 16 bits for a Cyclic Redundancy Check (CRC).
Physical resources transmitted over the PDCCH takes a Control Channel Element (CCE) as a unit, the size of which is nine Resource Element Groups (REG), i.e., 36 resource elements, and one PDCCH may occupy 1, 2, 4, or 8 CCEs. For four PDCCHs occupying 1, 2, 4, and 8 CCEs respectively, a tree aggregation is adopted, i.e., the PDCCH occupying 1 CCE may start from any CCE location; the PDCCH occupying 2 CCEs starts from an even CCE location; the PDCCH occupying 4 CCEs starts from a CCE location of an integer multiple of 4; and the PDCCH occupying 8 CCEs starts from a CCE location of an integer multiple of 8.
Each aggregation level defines a search space comprising a common search space and a user equipment specific (UE-specific) search space. The number of CCEs in the entire search space is determined by the number of OFDM symbols occupied by control areas indicated by the PCFICH in each downlink subframe and the number of groups of the PHICHs. The UE performs blind detection in the search space on all possible PDCCH bit rates based on a DCI format of a transmission mode of itself.
The UE is semi-statistically configured through high-level signaling to receive PDSCH data transmission according to an indication of a PDCCH in the UE-specific search space based on at least one of the following transmission modes:
Mode 1: Single-antenna port: port 0
Mode 2: Transmit diversity
Mode 3: Open-loop spatial multiplexing
Mode 4: Closed-loop spatial multiplexing
Mode 5: Multi-user Multiple-Input Multiple-Out-put (MIMO)
Mode 6: Closed-loop Rank=1 precoding
Mode 7: Single-antenna port: port 5
If the UE is configured by the high level to decode a PDCCH with a Cyclical Redundancy Check (CRC) scrambled with a Cell Radio Network Temporary Identifier (C-RNTI), then the UE should decode the PDCCH and all relevant PDSCHs according to a corresponding combination as defined in Table 1.
TABLE 1UE downlinkcorrespondingtransmissionPDSCH transmissionmodeDCI FormatSearch spacescheme of PDCCHMode 1DCI FormatCommon andSingle-antenna port:1AC-RNTI-definedport 0UE specificDCI FormatC-RNTI-definedSingle-antenna port:1UE specificport 0Mode 2DCI FormatCommon andTransmit diversity1AC-RNTI-definedUE specificDCI FormatC-RNTI-definedTransmit diversity1UE specificMode 3DCI FormatCommon andTransmit diversity1AC-RNTI-definedUE specificDCI FormatC-RNTI-definedOpen-loop spatial2AUE specificmultiplexing or transmitdiversityMode 4DCI FormatCommon andTransmit diversity1AC-RNTI-definedUE specificDCI FormatC-RNTI-definedClosed-loop spatial2UE specificmultiplexing or transmitdiversityMode 5DCI FormatCommon andTransmit diversity1AC-RNTI-definedUE specificDCI FormatC-RNTI-definedMulti-user MIMO1DUE specificMode 6DCI FormatCommon andTransmit diversity1AC-RNTI-definedUE specificDCI FormatC-RNTI-definedClosed-loop Rank =1BUE specific1 precodingMode 7DCI FormatCommon andIf the number of1AC-RNTI-definedPBCH antenna ports isUE specific1, using asingle-antenna port:port 0; otherwise,using transmit diversityDCI FormatC-RNTI-definedSingle-antenna port:1UE specificport 5
If the UE is configured by the high level to decode a PDCCH with a CRC scrambled by a Semi-Persistently Scheduled Cell Radio Network Temporary Identifier (SPS C-RNTI), then the UE should decode the PDCCH and all relevant PDSCHs according to a corresponding combination as defined in Table 2:
TABLE 2correspondingUE downlinkPDSCHtransmissiontransmissionmodeDCI FormatSearch spacescheme of PDCCHMode 1DCI FormatCommon andSingle-antenna1AC-RNTI-definedport: port 0UE specificDCI FormatC-RNTI-definedSingle-antenna1UE specificport: port 0Mode 2DCI FormatCommon andTransmit1AC-RNTI-defineddiversityUE specificDCI FormatC-RNTI-definedTransmit1UE specificdiversityMode 3DCI FormatCommon andTransmit1AC-RNTI-defineddiversityUE specificDCI FormatC-RNTI-definedTransmit2AUE specificdiversityMode 4DCI FormatCommon andTransmit1AC-RNTI-defineddiversityUE specificDCI FormatC-RNTI-definedTransmit2UE specificdiversityMode 5DCI FormatCommon andTransmit1AC-RNTI-defineddiversityUE specificMode 6DCI FormatCommon andTransmit1AC-RNTI defined-diversityUE specificMode 7DCI FormatCommon andSingle-antenna1AC-RNTI defined-port: port 5UE specificDCI FormatC-RNTI-definedSingle-antenna1UE specificport: port 5
Particularly, when the UE is configured to decode a PDCCH with a CRC scrambled by an SPS C-RNTI and semi-static scheduling is activated, information bits of the DCI Format 1A will change as follows:
(1) in the 5 bits for indicating a Modulation And Coding Scheme (MCS), the bit of the Most Significant Bit (MSB), i.e., the utmost left bit, will be set to be 0;
(2) the 3 bits for indicating HARQ process number in the FDD system and the 4 bits for indicating HARQ process number will be set to be 0;
(3) the 1 bit for a New Data Indicator (NDI) will be set to be 0;
(4) the 2 bits for indicating a Redundant Version (RV) will be set to be 0.
In the transmission mode 7, a single antenna port 5-based transmission is a non-codebook spatial multiplexing manner with Rank=1 and also is application of a single-layer beamforming technology; while currently, in order to enhance the performance of the downlink non-codebook transmission manner, a new transmission scheme is provided in the LTE enhanced version R9, which is a non-codebook spatial multiplexing manner with Rank=2, i.e., a dual-antenna-port transmission adopting a dual-layer beamforming technology.
Therefore, it is necessary to define a new transmission mode in R9 to correspond to the dual-layer beamforming technology. As defined in R8, this new transmission mode needs two DCI formats, wherein in the common search space and the C-RNTI-defined UE-specific search space, DCI Format 1A is required to be adopted. However, in the existing technical solution, a transmission scheme as well as how to indicate the transmission scheme are not determined in the DCI Format 1A, thereby bringing about inconvenience to practical application.